OpenJDK 6 Build README

This README file contains build instructions for the
OpenJDK.
Building the source code for the
OpenJDK
requires
a certain degree of technical expertise.

This document is specific to OpenJDK 6, which has some
very minor differences in the build requirements over
the OpenJDK 7 sources,
e.g. OpenJDK 6 requires access to Motif files.
Where there are differences they should stand out,
like this block of text does.

The OpenJDK sources are maintained with the revision control system
Mercurial.
If you are new to Mercurial, please see the
Beginner Guides
or refer to the Mercurial Book.
The first few chapters of the book provide an excellent overview of
Mercurial, what it is and how it works.
For using Mercurial with the OpenJDK refer to the
Developer Guide: Installing and Configuring Mercurial
section for more information.
The Forest Extension is not part of the Mercurial install,
and is optional,
but can be obtained with the following commands:

This file often describes specific requirements for what we call the
"minimum build environments" (MBE) for this
specific release of the JDK,
Building with the MBE will generate the most compatible
bits that install on, and run correctly on, the most variations
of the same base OS and hardware architecture.
These usually represent what is often called the
least common denominator platforms.
It is understood that most developers will NOT be using these
specific platforms, and in fact creating these specific platforms
may be difficult due to the age of some of this software.

The minimum OS and C/C++ compiler versions needed for building the
OpenJDK6:

Base OS and Architecture

OS

C/C++ Compiler

BOOT JDK

Linux X86 (32bit)

Fedora 9

gcc 4

JDK 6u18

Linux X64 (64bit)

Fedora 9

gcc 4

JDK 6u18

Solaris SPARC (32-bit)

Solaris 10 Update 6

Sun Studio 12 Update 1 + patches

JDK 6u18

Solaris SPARCV9 (64-bit)

Solaris 10 Update 6

Sun Studio 12 Update 1 + patches

JDK 6u18

Solaris X86 (32-bit)

Solaris 10 Update 6

Sun Studio 12 Update 1 + patches

JDK 6u18

Solaris X64 (64-bit)

Solaris 10 Update 6

Sun Studio 12 Update 1 + patches

JDK 6u18

Windows X86 (32bit)

Windows 2000

Microsoft Visual Studio .NET 2003 Professional

JDK 6u18

Windows X64 (64bit)

Windows Server 2003 - Enterprise x64 Edition

Microsoft Platform SDK - April 2005

JDK 6u18

These same sources do indeed build on many more systems than the
above older generation systems, again the above is just a minimum.

Compilation problems with newer or different C/C++ compilers is a
common problem.
Similarly, compilation problems related to changes to the
/usr/include or system header files is also a
common problem with newer or unreleased OS versions.
Please report these types of problems as bugs so that they
can be dealt with accordingly.

Ubuntu 8.04

After installing Ubuntu 8.04
you need to install several build dependencies.

First, you need to enable the universe repository in the
Software Sources application and reload the repository
information. The Software Sources application is available
under the System/Administration menu.

The simplest way to install the build dependencies is to
execute the following commands:

sudo aptitude build-dep openjdk-6

sudo aptitude install openjdk-6-jdk

sudo aptitude install libmotif-dev

In addition, it's necessary to set a few environment variables for the build:

export LANG=C ALT_BOOTDIR=/usr/lib/jvm/java-6-openjdk

Ubuntu 8.10

After installing Ubuntu 8.10
you need to install several build dependencies. The simplest
way to do it is to execute the following commands:

sudo aptitude build-dep openjdk-6

sudo aptitude install openjdk-6-jdk gcc-4.2 g++-4.2

sudo aptitude install libmotif-dev

In addition, it's necessary to set a few environment variables for the build:

export LANG=C ALT_BOOTDIR=/usr/lib/jvm/java-6-openjdk

Then, calling make in the top level OpenJDK source
code directory with the following parameters results in a
working build:

make all CC=gcc-4.2 CPP=g++-4.2

Ubuntu 9.04

After installing Ubuntu 9.04
you need to install several build dependencies. The simplest
way to do it is to execute the following commands:

sudo aptitude build-dep openjdk-6

sudo aptitude install openjdk-6-jdk gcc-4.2 g++-4.2

sudo aptitude install libmotif-dev

In addition, it's necessary to set a few environment variables for the build:

export LANG=C ALT_BOOTDIR=/usr/lib/jvm/java-6-openjdk

Then, calling make in the top level OpenJDK source
code directory with the following parameters results in a
working build:

The source code for the OpenJDK is delivered in a set of
directories:
hotspot,
langtools,
corba,
jaxws,
jaxp,
and
jdk.
The hotspot directory contains the source code and make
files for building the OpenJDK Hotspot Virtual Machine.
The langtools directory contains the source code and make
files for building the OpenJDK javac and language tools.
The corba directory contains the source code and make
files for building the OpenJDK Corba files.
The jaxws directory contains the source code and make
files for building the OpenJDK JAXWS files.
The jaxp directory contains the source code and make
files for building the OpenJDK JAXP files.
The jdk directory contains the source code and make files for
building the OpenJDK runtime libraries and misc files.
The top level Makefile
is used to build the entire OpenJDK.

The repositories jaxp and jaxws actually
do not contain the sources for JAXP or JAX-WS.
These products have their own open source procedures at their
JAXP and
JAX-WS home pages.
The OpenJDK project does need access to these sources to build
a complete JDK image because JAXP and JAX-WS are part of the JDK.
The current process for delivery of the JAXP and JAX-WS sources
involves so called "source drop bundles" downloaded from a public
website.
There are many reasons for this current mechanism, and it is
understood that this is not ideal for the open source community.
It is possible this process could change in the future.
NOTE: The
Complete OpenJDK Source Bundleswill contain the JAXP and
JAX-WS sources.

The JAXP or JAX-WS team prepares a new zip bundle,
places a copy in a public download area on java.net,
sends us a link and a list of CRs (Change Request Numbers).
The older download bundles should not be deleted.
It is the responsibility of the JAXP and JAX-WS team to
place the proper GPL legal notices on the sources
and do any filtering or java re-packaging for the
OpenJDK instances of these classes.

The OpenJDK team copies this new bundle into shared
area (e.g. /java/devtools/share/jdk6-drops).
Older bundles are never deleted so we retain the history.

The OpenJDK team edits the ant property file
jaxp/jaxp.properties or
jaxws/jaxws.properties to update the
base URL, the zip bundle name, and the MD5 checksum
of the zip bundle
(on Solaris: sum -c md5 bundlename)

The ant scripts that build jaxp and jaxws
will attempt to locate these zip bundles from the directory
in the environment variable
ALT_DROPS_DIR.
The checksums protect from getting the wrong, corrupted, or
improperly modified sources.
Once the sources are made available, the population will not
happen again unless a make clobber is requested
or the jaxp/drop/ or jaxws/drop/
directory is explicitly deleted.
NOTE: The default Makefile and ant script behavior
is to NOT download these bundles from the public http site.
In general, doing downloads
during the build process is not advised, it creates too much
unpredictability in the build process.
However, you can use make ALLOW_DOWNLOADS=true to
tell the ant script that the download of the zip bundle is
acceptable.

The recommended procedure for keeping a cache of these
source bundles would be to download them once, place them
in a directory outside the repositories, and then set
ALT_DROPS_DIR to refer
to that directory.
These drop bundles do change occasionally, so the newer
bundles may need to be added to this area from time to time.

Building the OpenJDK
is done with a GNU make command line
and various
environment or make variable settings that direct the make rules
to where various components have been installed.
Where possible the makefiles will attempt to located the various
components in the default locations or any component specific
variable settings.
When the normal defaults fail or components cannot be found,
the various
ALT_* variables (alternates)
can be used to help the makefiles locate components.

Refer to the bash/sh/ksh setup file
jdk/make/jdk_generic_profile.sh
if you need help in setting up your environment variables.
A build could be as simple as:

Of course ksh or sh would work too.
But some customization will probably be necessary.
The sanity rule will make some basic checks on build
dependencies and generate appropriate warning messages
regarding missing, out of date, or newer than expected components
found on your system.

The Makefiles in the OpenJDK are only valid when used with the
GNU version of the utility command make
(gmake).
A few notes about using GNU make:

You need GNU make version 3.81 or newer.

Place the location of the GNU make binary in the PATH.

Linux:
The /usr/bin/make should be 3.81 or newer
and should work fine for you.
If this version is not 3.81 or newer,
see the "Building GNU make" section.

Solaris:
Do NOT use /usr/bin/make on Solaris.
If your Solaris system has the software
from the Solaris Companion CD installed,
you should try and use gmake
which will be located in either the /opt/sfw/bin or
/usr/sfw/bin directory.
In more recent versions of Solaris GNU make might be found
at /usr/bin/gmake.NOTE: It is very likely that this gmake
could be 3.80, you need 3.81, in which case,
see the "Building GNU make" section.

Windows:
Make sure you start your build inside a bash/sh/ksh shell
and are using a make.exe utility built for that
environment (a cygwin make.exe is not the same
as a make.exe built for something like
MKS).
WARNING: Watch out on some make 3.81 versions, it may
not work due to a lack of support for MS-DOS drive letter paths
like C:/ or C:\.
You may be able to use the information at the
mozilla developer center
on this topic.
It's hoped that when make 3.82 starts shipping in a future cygwin
release that this MS-DOS path issue will be fixed.
It may be possible to download the version at
www.cmake.org make.exe.
It might be necessary for you to build your own GNU make 3.81,
see the "Building GNU make" section
in that case.

i586 only:
The minimum recommended hardware for building the Linux version
is a Pentium class processor or better, at least 256 MB of RAM, and
approximately 1.5 GB of free disk space.

X64 only:
The minimum recommended hardware for building the Linux
version is an AMD Opteron class processor, at least 512 MB of RAM, and
approximately 4 GB of free disk space.

The build will use the tools contained in
/bin and
/usr/bin
of a standard installation of the Linux operating environment.
You should ensure that these directories are in your
PATH.

Note that some Linux systems have a habit of pre-populating
your environment variables for you, for example JAVA_HOME
might get pre-defined for you to refer to the JDK installed on
your Linux system.
You will need to unset JAVA_HOME.
It's a good idea to run env and verify the
environment variables you are getting from the default system
settings make sense for building the
OpenJDK.

The minimum recommended hardware for building the
Solaris SPARC version is an UltraSPARC with 512 MB of RAM.
For building
the Solaris x86 version, a Pentium class processor or better and at
least 512 MB of RAM are recommended.
Approximately 1.4 GB of free disk
space is needed for a 32-bit build.

If you are building the 64bit version, you should
run the command "isainfo -v" to verify that you have a
64-bit installation, it should say sparcv9 or
amd64.
An additional 7 GB of free disk space is needed
for a 64-bit build.

The build uses the tools contained in /usr/ccs/bin
and /usr/bin of a standard developer or full installation of
the Solaris operating environment.

Solaris patches specific to the JDK can be downloaded from the
SunSolve JDK Solaris patches download page.
You should ensure that the latest patch cluster for
your version of the Solaris operating environment has also
been installed.

i586 only:
The minimum recommended hardware for building the 32bit or X86
Windows version is an Pentium class processor or better, at least
512 MB of RAM, and approximately 600 MB of free disk space.
NOTE: The Windows 2000 build machines need to use the
file system NTFS.
Build machines formatted to FAT32 will not work
because FAT32 doesn't support case-sensitivity in file names.

X64 only:
The minimum recommended hardware for building
the Windows X64 version is an AMD Opteron class processor, at least 1
GB of RAM, and approximately 10 GB of free disk space.

Windows:
Note that GNU make is a historic utility and is based very
heavily on shell scripting, so it does not tolerate the Windows habit
of having spaces in pathnames or the use of the \characters in pathnames.
Luckily on most Windows systems, you can use /instead of \, and
there is always a 'short' pathname without spaces for any path that
contains spaces.
Unfortunately, this short pathname can be somewhat dynamic and the
formula is difficult to explain.
You can use cygpath utility to map pathnames with spaces
or the \character into the C:/ style of pathname
(called 'mixed'), e.g.
cygpath -s -m "path".

The makefiles will try to translate any pathnames supplied
to it into the C:/ style automatically.

Note that use of CYGWIN creates a unique problem with regards to
setting PATH. Normally on Windows
the PATH variable contains directories
separated with the ";" character (Solaris and Linux uses ":").
With CYGWIN, it uses ":", but that means that paths like "C:/path"
cannot be placed in the CYGWIN version of PATH and
instead CYGWIN uses something like /cygdrive/c/path
which CYGWIN understands, but only CYGWIN understands.
So be careful with paths on Windows.

Depending on the platform, the OpenJDK build process has some basic
dependencies on components not part of the OpenJDK sources.
Some of these are specific to a platform, some even specific to
an architecture.
Each dependency will have a set of ALT variables that can be set
to tell the makefiles where to locate the component.
In most cases setting these ALT variables may not be necessary
and the makefiles will find defaults on the system in standard
install locations or through component specific variables.

All OpenJDK builds require access to the previously released
JDK 6, this is often called a bootstrap JDK.

Normally the "boot" JDK is the previously released version
of the JDK, so it's unusual for a JDK 6 build like this to
require a JDK 6 "boot".
Unfortunately, it is currently required due to some JDK 6
dependencies in some of the sources.

The JDK 6 binaries can be downloaded from Sun's
JDK 6 download site.
For build performance reasons
is very important that this bootstrap JDK be made available on the
local disk of the machine doing the build.
You should always set
ALT_BOOTDIR
to point to the location of
the bootstrap JDK installation, this is the directory pathname
that contains a bin, lib, and include
It's also a good idea to also place its bin directory
in the PATH environment variable, although it's
not required.

Solaris:
Some pre-installed JDK images may be available to you in the
directory /usr/jdk/instances.
If you don't set
ALT_BOOTDIR
The makefiles will look in that location for a JDK it can use.

Linux:
Many GNU/Linux distributions already include OpenJDK 6. OpenJDK 6
can be used to bootstrap itself, so installing the corresponding
distribution package is sufficient. You'll still need to set
ALT_BOOTDIR, though.

The ALT_JDK_IMPORT_PATH
setting is only needed if you are not building the entire
JDK. For example, if you have built the entire JDK once, and
wanted to avoid repeatedly building the Hotspot VM, you could
set this to the location of the previous JDK install image
and the build will copy the needed files from this import area.

All OpenJDK builds require access to least Ant 1.7.1.
The Ant 1.7.1 tool is available from the
Ant 1.7.1 archive download site.
You should always make sure ant is in your PATH, and
on Windows you may also need to set
ANT_HOME
to point to the location of
the Ant installation, this is the directory pathname
that contains a bin and lib.
WARNING: Ant versions used from IDE tools like NetBeans
or installed via system packages may not operate the same
as the one obtained from the Ant download bundles.
These system and IDE installers sometimes choose to change
the ant installation enough to cause differences.

See
http://en.wikipedia.org/wiki/Certificate_Authority
for a better understanding of the Certificate Authority (CA).
A certificates file named "cacerts"
represents a system-wide keystore with CA certificates.
In JDK and JRE
binary bundles, the "cacerts" file contains root CA certificates from
several public CAs (e.g., VeriSign, Thawte, and Baltimore).
The source contain a cacerts file
without CA root certificates.
Formal JDK builders will need to secure
permission from each public CA and include the certificates into their
own custom cacerts file.
Failure to provide a populated cacerts file
will result in verification errors of a certificate chain during runtime.
The variable
ALT_CACERTS_FILE
can be used to override the default location of the
cacerts file that will get placed in your build.
By default an empty cacerts file is provided and that should be
fine for most JDK developers.

The 32-bit OpenJDK Windows build
requires Microsoft Visual Studio .NET 2003 (VS2003) Professional
Edition compiler.
The compiler and other tools are expected to reside
in the location defined by the variable VS71COMNTOOLS which
is set by the Microsoft Visual Studio .NET installer.

Once the compiler is installed,
it is recommended that you run VCVARS32.BAT
to set the compiler environment variables
MSVCDIR,
INCLUDE,
LIB, and
PATH
prior to building the
OpenJDK.
The above environment variables MUST be set.

These bat files are not easy to use from a shell environment.
There is a script placed in the root jdk6 repository called
vsvars.sh that can help, it should only be done once in a shell
that will be doing the build, e.g.sh ./make/scripts/vsvars.sh -v7 > settings
eval `cat settings`
Or just eval `sh ./make/scripts/vsvars.sh -v7`.

The Microsoft Visual Studio .NET 2005 (VS2005) compiler
will not work at this time due to the new runtime dll
and the manifest requirements.

On X64, the Microsoft Platform Software
Development Kit (SDK), April 2005 Edition compiler,
is required for building the OpenJDK
because it contains the C/C++ compiler.
You will need to minimally install the Core SDK and
the MDAC SDK features of this compiler.

Once the Platform SDK is installed,
it is recommended that you run SetEnv.Cmd /X64
to set the compiler environment variables
MSSDK,
MSTOOLS,
INCLUDE,
LIB, and
PATH
prior to building the
OpenJDK.
The above environment variables MUST be set.

Note that this compiler may say it's version is a
Microsoft Visual Studio .NET 2005 (VS2005), but be careful,
it will not match the official VS2005 product.
This Platform SDK compiler is only used on X64 builds.

Version 2.2 (November 3rd 1997) or newer of the zip utility
and version 5.12 or newer of the unzip utility is needed
to build the JDK.
With Solaris, Linux, and Windows CYGWIN, the zip and unzip
utilities installed on the system should be fine.
Information and the source code for
ZIP.EXE and UNZIP.EXE is available on the
info-zip web site.

Solaris:
CUPS header files are required for building the
OpenJDK on Solaris.
The Solaris header files can be obtained by installing
the package SFWcups from the Solaris Software
Companion CD/DVD, these often will be installed into
/opt/sfw/cups.

Linux:
CUPS header files are required for building the
OpenJDK on Linux.
The Linux header files are usually available from a "cups"
development package, it's recommended that you try and use
the package provided by the particular version of Linux that
you are using.

The CUPS header files can always be downloaded from
www.cups.org.
The variable
ALT_CUPS_HEADERS_PATH
can be used to override the default location of the
CUPS Header files.

Motif headers (not libraries) are required for building the
OpenJDK 6.

Solaris:
Normally these files can be found on Solaris systems
at /usr/include/Xm, so on Solaris systems no further downloads
should be needed.

Linux:
On Linux, your particular Linux distribution may provide a
"motif" development package you can install. If this package
installs the files into /usr/include/Xm, no further action should
be needed.
An acceptable version of these Motif header files are
available in the source bundle
openmotif-2.1.30.5p1.tgz
from
www.openbsd.org.
You would need to install the package and set the environment variable
ALT_MOTIF_DIR
to refer to the top of this installation.

Version 2.3 or newer of FreeType is required for building the OpenJDK.
On Unix systems required files can be available as part of your
distribution (while you still may need to upgrade them).
Note that you need development version of package that
includes both FreeType library and header files.

Makefiles will try to pick FreeType from /usr/lib and /usr/include.
In case it is installed elsewhere you will need to set environment
variables
ALT_FREETYPE_LIB_PATH
and
ALT_FREETYPE_HEADERS_PATH
to refer to place where library and header files are installed.

Linux only:
Version 0.9.1 or newer of the ALSA files are
required for building the OpenJDK on Linux.
These Linux files are usually available from an "alsa"
of "libasound"
development package, it's highly recommended that you try and use
the package provided by the particular version of Linux that
you are using.
The makefiles will check this emit a sanity error if it is
missing or the wrong version.

In particular, older Linux systems will likely not have the
right version of ALSA installed, for example
Redhat AS 2.1 U2 and SuSE 8.1 do not include a sufficiently
recent ALSA distribution.
On rpm-based systems, you can see if ALSA is installed by
running this command:

rpm -qa | grep alsa

Both alsa and alsa-devel packages are needed.

If your distribution does not come with ALSA, and you can't
find ALSA packages built for your particular system,
you can try to install the pre-built ALSA rpm packages from
www.freshrpms.net.
Note that installing a newer ALSA could
break sound output if an older version of ALSA was previously
installed on the system, but it will enable JDK compilation.

Microsoft DirectX 9.0 SDK (Summer 2004)
headers are required for building
OpenJDK.
This SDK can be downloaded from
Microsoft DirectX 9.0 SDK (Summer 2004).
If the link above becomes obsolete, the SDK can be found from
the Microsoft Download Site
(search with "DirectX 9.0 SDK Update Summer 2004").
The location of this SDK can be set with
ALT_DXSDK_PATH
but it's normally found via the DirectX environment variable
DXSDK_DIR.

i586 only:
The OpenJDK 32bit build requires access to
MSVCRT.DLL version 6.00.8337.0 or newer.
If the MSVCRT.DLL is not installed in
the system32 directory set the
ALT_MSVCRT_DLL_PATH
variable to the location.

X64 only:
The OpenJDK 64bit build requires access to
MSVCRT.DLL version 7.0.3790.0 or newer, which is
usually supplied by the
Platform SDK.
If it is not available from the Platform SDK,
set the
ALT_MSVCRT_DLL_PATH
variable to the location.

i586 only:
The
OpenJDK
build requires access to
MSVCR71.DLL version 7.10.3052.4 or newer which should be
supplied by the
Visual Studio product
If the MSVCR71.DLL is not available from the
Visual Studio product
set the
ALT_MSVCR71_DLL_PATH
variable to the location.

Solaris:
Note that ARCH_DATA_MODEL is really only needed on Solaris to
indicate you want to built the 64-bit version.
And before the Solaris 64-bit binaries can be used, they
must be merged with the binaries from a separate 32-bit build.
The merged binaries may then be used in either 32-bit or 64-bit mode, with
the selection occurring at runtime
with the -d32 or -d64 options.

When the build is completed, you should see the generated
binaries and associated files in the j2sdk-image
directory in the output directory.
The default output directory is
build/platform,
where platform is one of

solaris-sparc

solaris-sparcv9

solaris-i586

solaris-amd64

linux-i586

linux-amd64

windows-i586

windows-amd64

In particular, the
build/platform/j2sdk-image/bin
directory should contain executables for the
OpenJDK tools and utilities.

You can test that the build completed properly by using the build
to run the various demos that you will find in the
build/platform/j2sdk-image/demo
directory.

The provided regression tests can be run with the jtreg
utility from
the jtreg site.

The ARCH_DATA_MODEL variable
is used to specify whether the build is to generate 32-bit or 64-bit
binaries.
The Solaris build supports either 32-bit or 64-bit builds, but
Windows and Linux will support only one, depending on the specific
OS being used.
Normally, setting this variable is only necessary on Solaris.
Set ARCH_DATA_MODEL to 32 for generating 32-bit binaries,
or to 64 for generating 64-bit binaries.

The location of tools like the
zip and unzip
binaries, but might also contain the GNU make utility
(gmake).
So this area is a bit of a grab bag, especially on Windows.
The default value depends on the platform and
Unix Commands being used.
On Linux the default will be
$(ALT_JDK_DEVTOOLS_PATH)/linux/bin,
on Solaris
$(ALT_JDK_DEVTOOLS_PATH)/{sparc,i386}/bin,
on Windows with MKS
%SYSTEMDRIVE%/UTILS,
and on Windows with CYGWIN
/usr/bin.

An override for specifying where the
Unix command set are located.
The default location varies depending on the platform,
"%SYSTEMDRIVE%/MKSNT" or
$(ROOTDIR) on Windows with MKS, otherwise it's
"/bin" or /usr/bin.

These are useful in managing builds on multiple platforms.
The default network location for all of the import JDK images
for all platforms.
If ALT_JDK_IMPORT_PATH
is not set, this directory will be used and should contain
the following directories:
solaris-sparc,
solaris-i586,
solaris-sparcv9,
solaris-amd64,
linux-i586,
linux-amd64,
windows-i586,
and
windows-amd64.
Where each of these directories contain the import JDK image
for that platform.

A build can fail for any number of reasons.
Most failures
are a result of trying to build in an environment in which all the
pre-build requirements have not been met.
The first step in
troubleshooting a build failure is to recheck that you have satisfied
all the pre-build requirements for your platform.
Look for the check list of the platform you are building on in the
Table of Contents.

You can validate your build environment by using the sanity
target.
Any errors listed
will stop the build from starting, and any warnings may result in
a flawed product build.
We strongly encourage you to evaluate every
sanity check warning and fix it if required, before you proceed
further with your build.

Some of the more common problems with builds are briefly described
below, with suggestions for remedies.

Corrupted Bundles on Windows:

Some virus scanning software has been known to corrupt the
downloading of zip bundles.
It may be necessary to disable the 'on access' or 'real time'
virus scanning features to prevent this corruption.
This type of "real time" virus scanning can also slow down the
build process significantly.
Temporarily disabling the feature, or excluding the build
output directory may be necessary to get correct and faster builds.

Slow Builds:

If your build machine seems to be overloaded from too many
simultaneous C++ compiles, try setting the HOTSPOT_BUILD_JOBS
variable to 1 (if you're using a multiple CPU
machine, setting it to more than the the number of CPUs is probably
not a good idea).

Creating the javadocs can be very slow, if you are running
javadoc, consider skipping that step.

Faster hardware and more RAM always helps too.
The VM build tends to be CPU intensive (many C++ compiles),
and the rest of the JDK will often be disk intensive.

Warning message: File `xxx' has modification time in
the future.Warning message: Clock skew detected. Your build may
be incomplete.

These warnings can occur when the clock on the build machine is out of
sync with the timestamps on the source files. Other errors, apparently
unrelated but in fact caused by the clock skew, can occur along with
the clock skew warnings. These secondary errors may tend to obscure the
fact that the true root cause of the problem is an out-of-sync clock.
For example, an out-of-sync clock has been known to cause an old
version of javac to be used to compile some files, resulting in errors
when the pre-1.4 compiler ran across the new assert keyword
in the 1.4 source code.

If you see these warnings, reset the clock on the build
machine, run "gmake clobber" or delete the directory
containing the build output, and restart the build from the beginning.

Error message: Trouble writing out table to disk

Increase the amount of swap space on your build machine.

Error Message: libstdc++ not found:

This is caused by a missing libstdc++.a library.
This is installed as part of a specific package
(e.g. libstdc++.so.devel.386).
By default some 64bit Linux versions (e.g. Fedora)
only install the 64bit version of the libstdc++ package.
Various parts of the JDK build require a static
link of the C++ runtime libraries to allow for maximum
portability of the built images.